Risk of increasing soil nitrous oxide emissions by chemical oxidation modification on biochar

Biochar is widely recognized as a soil amendment capable of mitigating soil nitrous oxide (N₂O) emissions. However, the effects of biochar modification, particularly through chemical oxidation, remain relatively unexplored. This study modified wood and corn straw biochars using H₂O₂ and acid (H₂SO₄/HNO₃). Laboratory incubations were conducted to assess their effects on N₂O emissions in agricultural and forest soils. The results revealed that acid modification significantly reduced biochar pH (<3) and introduced additional nitrogen, leading to substantial increases in N₂O emissions by up to 181% and 7476% for wood and corn straw biochar, respectively. In contrast, H₂O₂-treated biochar caused limited changes in biochar properties and had minimal effects on soil N₂O emissions. Correlation analyses suggest distinct pathways for N₂O production, with forest soil emissions being negatively associated with potential denitrification enzyme activity, while agricultural soil emissions were positively linked to labile organic carbon and potential nitrification rates. While mild oxidation (e.g., H₂O₂) may better mimic natural aging process, stronger treatments (e.g., acid oxidation) pose risks of increased soil N₂O emissions. This study provides valuable insights for optimizing biochar modifications to balance environmental and ecological benefits.